This invention relates to vitamin D compounds, and more particularly to pharmaceutical uses for 2.alpha.(-methyl-19-nor-20(S)-1.alpha.,25-dihydroxyvitamin D.sub.3.
The natural hormone, 1.alpha.,25-dihydroxyvitamin D.sub.3 and its analog in ergocalciferol series, i.e. 1.alpha.,25-dihydroxyvitamin D.sub.2 are known to be highly potent regulators of calcium homeostasis in animals and humans, and more recently their activity in cellular differentiation has been established, Ostrem et al., Proc. Natl. Acad. Sci. USA, 84, 2610 (1987). Many structural analogs of these metabolites have been prepared and tested, including 1.alpha.-hydroxyvitamin D.sub.3, 1.alpha.-hydroxyvitamin D.sub.2, various side chain homologated vitamins and fluorinated analogs. Some of these compounds exhibit an interesting separation of activities in cell differentiation and calcium regulation. This difference in activity may be useful in the treatment of a variety of diseases as renal osteodystrophy, vitamin D-resistant rickets, osteoporosis, psoriasis, and certain malignancies.
Recently, a new class of vitamin D analogs has been discovered, i.e. the so called 19-nor-vitamin D compounds, which are characterized by the replacement of the A-ring exocyclic methylene group (carbon 19), typical of the vitamin D system, by two hydrogen atoms. Biological testing of such 19-nor-analogs (e.g., 1.alpha.,25-dihydroxy-19-nor-vitamin D.sub.3) revealed a selective activity profile with high potency in inducing cellular differentiation, and very low calcium mobilizing activity. Thus, these compounds are potentially useful as therapeutic agents for the treatment of malignancies, or the treatment of various skin disorders. Two different methods of synthesis of such 19-nor-vitamin D analogs have been described (Perlman et al., Tetrahedron Lett. 31, 1823 (1990); Perlman et al., Tetrahedron Lett. 32, 7663 (1991), and DeLuca et al., U.S. Pat. No. 5,086,191).
In U.S. Pat. No. 4,666,634, 2.beta.-hydroxy and alkoxy (e.g., ED-71) analogs of 1.alpha.,25-dihydroxyvitamin D.sub.3 have been described and examined by Chugai group as potential drugs for osteoporosis and as antitumor agents. See also Okano et al., Biochem. Biophys. Res. Commun. 163, 1444 (1989). Other 2-substituted (with hydroxyalkyl, e.g., ED-120, and fluoroalkyl groups) A-ring analogs of 1.alpha.,25-dihydroxyvitamin D.sub.3 have also been prepared and tested (Miyamoto et al., Chem. Pharm. Bull. 41, 1111 (1993); Nishii et al., Osteoporosis Int. Suppl. 1, 190 (1993); Posner et al., J. Org. Chem. 59, 7855 (1994), and J. Org. Chem. 60, 4617 (1995)).
Recently, 2-substituted analogs of 1.alpha.,25-dihydroxy-19-nor-vitamin D.sub.3 have also been synthesized, i.e. compounds substituted at 2-position with hydroxy or alkoxy groups (DeLuca et al., U.S. Pat. No. 5,536,713), which exhibit interesting and selective activity profiles. All these studies indicate that binding sites in vitamin D receptors can accommodate different substituents at C-2 in the synthesized vitamin D analogs.
In a continuing effort to explore the 19-nor class of pharmacologically important vitamin D compounds, an analog which is characterized by the presence of a methyl substituent at the carbon 2 (C-2) has been synthesized and tested. Of particular interest is the analog which is characterized by the unnatural configuration of the methyl group at carbon 20 (C-20), i.e. 2.alpha.-methyl-19-nor-20(S)-1.alpha.,25-dihydroxyvitamin D.sub.3. This vitamin D analog seemed an interesting target because the relatively small methyl group at C-2 should not interfere with the vitamin D receptor. Moreover, molecular mechanics studies performed on the model 1.alpha.-hydroxy-2-methyl-19-nor-vitamins indicate that such molecular modification does not change substantially the conformation of the cyclohexanediol ring A. However, introduction of the 2-methyl group into 19-nor-vitamin D carbon skeleton changes the character of its 1.alpha.- and 3.beta.- A-ring hydroxyls. Both hydroxyls are allylic to the exocyclic methylene group similar to the 1.alpha.-hydroxyl group (crucial for biological activity) in the molecule of the natural hormone, 1.alpha.,25-(OH).sub.2 D.sub.3.